Distillation of high boiling hydrocarbons and products therefrom



Jan. 18, 1955 c. NAUMANN 2,700,016

- DISTILLATION OF HIGH BOILING HYDROCARBONS AND PRODUCTS THEREFROM Filed NOV. 27, 1950 4 Sheqts-Sheet 1 H01- NLUTRALGAB 727 l I w.

Ham/Y HY DROCARBON DisnLLAT'oN PRODUCTS H EAVY HYDROCARBON Census-nan:

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Am \L HEAVYHYDROQARBON ComBus'nsLa 4 INVENTOR Jan. 18, 1955 c. NAUMANN 2,700,016

DISTILLATION OF HIGH BOILING HYDROCARBONS I AND PRODUCTS THEREFROM Filed Nov. 2'7, 1950 4 Sheets-Sheet 2 INVENTOR Wcuaviafln L] GREYS c. NAUMANN DISTILLATION OF HIGH BOILING HYDROCARBONS Jan. 18, 1955 AND PRODUCTS THEREFROM 4 Sheets-Sheet 5 Filed NOV. 27. 1950 00 00 000 O O O 0 0 my %W 00 iNVENTOR 614,236 Wamann ATTQRNEYS.

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Jan. 18, 1955 c. NAUMANN DISTILLATION OF HIGH BOILING HYDROCARBON AND PRODUCTS THEREFROM 4 Sheets-Sheet. 4

Filed NOV. 27, 1950 n 8 l. v N H in? 5 m C m wv fi :mmi .v w llll lllklllvlllf lu 0 WIN United States Patent DISTILLATIQN OF HHGH BOILING HYDRO- CARBGNS AND PRQDUCTS THEREFROM Carl Naumann, Philadelphia, Pa.

Application November 27, 1950, Serial No. 197,720

Claims. (Cl. 19684) The present invention relates to the distillation of high boiling (above 170 C. and more usually above 200 C.) hydrocarbons and the products obtained therefrom.

The invention is particularly concerned with a distillation process to recover more distillate and less coke residue than by conventional methods of distilling high boiling hydrocarbons. The distillation is essentially a high temperature high velocity low pressure distillation system in which the heat for distillation is rapidly and thoroughly internally disseminated by an essentially neutral gas throughout the bath of material being distilled with a minimum of partial polymerization.

A purpose of the invention is to obtain a higher yield of distillate from hydrocarbons boiling over 170 C. than that which has been possible from existing processes.

A further purpose is to distill high boiling hydrocarbons quite completely at lower temperatures.

A further purpose is to reduce the time required to distill high boiling hydrocarbons.

A further purpose is to make it possible to distill, with internal heat, high boiling, especially high gravity, hydrocarbons which are solid or semi-solid at normal temperatures.

A further purpose is to distill these high boiling hydrocarbons with less thermal decomposition than results from convecting heat from an external heat source through the container walls into the material being distilled.

A further purpose is to rapidly heat the materials being distilled to distillation temperatures by passing through them a very hot gas, neutral to the material being distilled with or without reheating and recycling.

A further purpose is to rapidly carry off the volatilized distillate with the heating gas to a condenser or series of condensers for removing the distillate.

A further purpose is to obtain an improved product known as carbon wax from heavy hydrocarbons.

A further purpose is to secure a more porous friable end product coke mass by distilling heavy hydrocarbons.

A further purpose is to recirculate non-condensible hydrocarbons obtained by distilling high boiling hydrocarbons back through the high boiling hydrocarbons being distilled, the recirculation medium being a gas which also acts as the heating medium and is desirably of inert character.

A further purpose is to condense high boiling distillates which at normal temperatures are greasy or wax-like in nature and thus likely to plug up the customary worm condenser cooled in a liquid bath.

A further purpose is to aid in condensation of the distillation products by successively expanding, cooling and condensing, then constricting and again expanding, cooling and condensing.

A further purpose is to distill high boiling hydrocarbons by recirculating a gas preferably of neutral character and most desirably predominantly or substantially entirely nitrogen continuously through the high boiling hydrocarbon, initially heating the gas sufiiciently to distill all the volatiles and preferably to a temperature of be tween 800 and 1,400 C. before it enters high boiling hydrocarbon, passing the initially heated gas through the high boiling hydrocarbon and heating the high boiling hydrocarbon wholly by the heat of the gas to a maximum still head temperature in excess of 250 C. and desirably to 345 C. in the case of tar and pitch, expanding and cooling the gas leaving the high boiling hydrocarbon with the distillation products and condensing condensible products, desirably successively going through the cycle of exice panding, condensing and then constricting before again expanding, compressing the gas and non-condensible products and then returning the gas for reheating in a closed system.

A further purpose is to continue the recirculation as above described until condensible distillate substantially ceases to come ofi and the resulting end product coke sets and then discontinuing the recirculation of the gas through the high boiling hydrocarbon and collecting the gaseous effluent given oil spontaneously by the heated coke.

A further purpose after the above steps is to blow air or steam through the residual heated coke and collect the gas thus formed.

1 Further purposes appear in the specification and in the c aims.

In the drawings I have chosen to illustrate a few only' of the numerous embodiments of equipment which may carry out the invention and of diagrams of the steps employed, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Figure 1, 2 and 3 are block diagrams useful in explaining the invention.

Figure 4 is a diagrammatic view of the preferred apparatus employed.

Figure 5 is a diagrammatic central vertical section of a variant form of preheater.

Figure 6 is a diagrammatic view of a detailed embodiment of the preferred apparatus.

Describing in illustration but not in limitation and referring to the drawings:

When reference is made herein to high boiling hydrocarbons it is intended to designate hydrocarbons which at the temperature of distillation will partially break down into carbon and volatile hydrocarbons of lower molecular weight. High boiling hydrocarbons are those which boil above 170 C. (they usually boil above 200 C.). Examples of high boiling hydrocarbons are coal tar, water-gas tar, coal tar pitch, water-gas pitch, pitch of animal origin, pitch of vegetable origin, heavy petroleum products such as petroleum tars and pitch, and heavy waxes of the character referred to as carbon wax. These heavy hydrocarbons have the common property of leaving a residue of coke in the distillation vessel if completely distilled, and producing condensible distillation products. They are often the residues of primary distillations of crude materials containing lighter bodied distillates.

Most of the prior distillation methods applied to high boiling hydrocarbons have involved external heating of a metallic still to obtain sufficient heat for distillation.

1 The temperature required has been high enough to cause steam, and of stopping the distillation when the residue contains from 5 to 15 percent of volatiles, which are subsequently separately removed if desired by calcining in a furnace.

Efforts have been made to improve on these externally heated stills by passing combustion gas at elevated temperature directly through high boiling hydrocarbons in a refractory still (Faben U. S. Patents No. 1,907,767 and 1,925,438). This process presents the difiiculty that combustion gases are present and oxidation is likely to occur; the resulting coke still requires removal for calcining if a volatile content less than 1 percent is desired; the recoverable distillate is limited to about 60 percent and is contaminated by combustion gases and the worm condensing apparatus is likely to be plugged by condensate from the products boiling 01f over 355 C. in externally fired stills.

Weiss U. S. Patent No. 1,418,893 describes a process which circulates moderately preheated air through an externally heated still to agitate the tar as it is distilled. The air is only sufficiently heated to avoid cooling. The apparatus for condensing is likely to clog from the products boiling off over 355 C. in externally fired stills.

Miller U. S. Patent No. 1,944,523 passes hot coke oven gas into heat transfer relation with high boiling hydrocarbon, throwing the hydrocarbon up into the path of the hot gas but without blowing the gas through the bath of hydrocarbon. The gas makes a single pass without recirculation.

In accordance with the present invention, the high boiling hydrocarbon is distilled by recirculating gas continuously through the hydrocarbon, preheating the gas sufliciently to distill off all the volatiles before it enters the hydrocarbon, passing the preheated gas through the hydrocarbon and heating the hydrocarbon wholly by the heat of the gas, then condensing the condensible products, and returning the gas and non-condensed products for reheating. The gas used is preferably a neutral or inert gas and desirably predominantly or preferably substantially entirely nitrogen, and the initial heating is desirably carried to a temperature between 800 and 1400 C., preferably between 1000 and 1100 C. The maximum still head temperature is in excess of 250 C. and up-to 345 C. in the case of tar and pitch. The condensation is accomplished in the preferred embodiment by expanding the gas containing the distillation products while cooling it and preferably repeating this several times, passing the gas through a constriction between the steps.

After condensible distillate substantially ceases to come off and the end product coke sets, the recirculation of the gas is desirably discontinued and a spontaneously evolved hydrocarbon gas is collected. When the evolution of this hydrocarbon has ceased, raw air or steam is desirably blown through the heated coke and the gas thus formed is collected.

The end product coke is calcined to less than 1 percent residual volatiles in the invention. Whereas under externally heated still practice in the prior art, 50 percent of the weight of the coal tar distilled came 01f as volatiles at 355 C., still head vapor temperature, in the process of the present invention, 70 percent comes off at 345 C., still head vapor tempearture. Thus the recovery of distillate is greater than in the prior art by from to 20 percent, and this recovery is accomplished at lower temperature.

Elfeetive distillation can also be carried out at lower temperature and accordingly with less destructive distillation or cracking than was obtained in the prior art.

A novel black wax product is obtained by the present invention which has advantageous properties in many fields, including the paint, rubber and ink field.

In accordance with the invention the distillation is carried out in three stages as shown in Figures 1 to 3 inclusive. The main distillation and separation of condensible products is accomplished in accordance with Figure 1. As shown in this figure the mass of high boiling hydrocarbon being distilled has continuously recirculated through it a hot neutral gas. As the gas leaves the still, it is cooled and preferably specially manipulated by successive expansions to condense and remove therefrom the condensible products, and is then again compressed and reheated to be recirculated through the high boiling hydrocarbon.

After the removal of the condensible products, the system is operated in accordance with Figure 2, in which a combustible hydrocarbon gas residue is collected. When the evolution of this hydrocarbon gas ceases, raw air or steam is blown through the heated high boiling hydrocarbon as shown in Figure 3, and a combined hydrocarbon and carbon monoxide gas is obtained. The resulting coke as later explained contains less than 1 percent of volatiles and does not require further calcining.

The apparatus which may be desirably employed is illustrated in Figure 4. A still 20 contains a bath of high boiling hydrocarbon 21 in the bottom and has any suitable charging and discharging and access openings 22 covered with doors as well known. The still is desirably lined with a suitable refractory such as silica brick (not shown), although any other suitable refractory such as fire clay brick, chrome brick or magnesia brick may be employed. A preheater 23 sup plies heated gas through a pipe 24 to tuyeres 25 whose nozzles are located inside the still 20 beneath the level of the high boiling hydrocarbon bath therein. Thus gas discharged through the tuyeres blows up through the high boiling hydrocarbon, substantially through the entire height of the same, from approximately the bottom of the still.

The preheater may take one of several forms as shown, the preferred embodiment being a recuperator as indicated in Figure 4. The recuperator consists of a cornbustion gas tube 26 which receives fuel gas at elevated temperature from a furnace 27 through a pipe 23 suitably connecting at the top of the recuperator and discharges it suitably at the bottom through a pipe 30 to a stack 31. The tube 26 through which heat transfer takes place is desirably of silicon carbide or other highly heat conductive material. The fuel burned with air in the furnace 27 may be of any suitable character, which will give the intensity of heat required, such as coal, coke, gas or oil.

Surrounding the heat transfer tube 26 is a gas jacket 32 free of combustion gas which receives gas suitably at the bottom through a pipe 33 and discharges it at the top to the pipe 24 connecting with the tuyeres 25 in the still.

The gas used will to great advantage be a neutral or inert gas which will not cause oxidation in the still and condensing system and will not support combustion during the distillation cycle. This is a matter of great importance. The preferred gas will be substantially all nitrogen or predominantly nitrogen with carbon dioxide and carbon monoxide forming minor constituents. If air is introduced at the beginning of the cycle and is continuously recirculated, the oxygen in the air will be oxidized to oxides of carbon, and water, and the residual gas will be substantially of the character above described. It is entirely proper, however, except for the expense, to introduce nitrogen or externally combusted air at the beginning of the cycle. It should be emphasized, however, that it is important to avoid continuous contact with combustion gases, and one advantage of the present invention is that contamination with free oxygen, sulphur, and other harmful ingredients of combustible gases is avoided after the very beginning of the cycle.

In some cases it may be preferred to use some other type of preheater which avoids mixing of gases. The form of Figure 5 illustrates conventionally a pebble heater 23 of any well known type. Fuel and air are introduced at 34 and burned in an upper chamber 34 in contact with pebbles 35. The combustion gases leave at the top by a stack 31. The heated pebbles drop down through a throat 35 into a lower chamber 32' where they pass in contact with recirculating gases introduced by pipe 33 and withdrawn by pipe 24. The pebbles are removed from the bottom of chamber 32 and returned to the top of chamber 35 by a pebble elevator 36, well known in the art.

A slightly greater pressure on the recirculating gas than on the combustion gas is maintained to avoid intermingling of the gases, any leakage being from the recirculating gas into the fuel combustion gas.

The gas in the preheater, whether it be a recuperator or pebble heater or other type, will desirably be heated to a high enough temperature to cause effective distillation. It is best to use a temperature range between 800 and 1400 C., the preferred range being between 1000 and 1100 C. for the temperature of the heating gas in the recuperator. The higher temperatures in this range are preferred as giving quicker heat transfer and less cracking of the high boiling hydrocarbons. \Vhile single pass recuperators have been shown, it will be understood that the number of passes in the recuperator may vary according to the preference of the designer.

The still head temperature will build up as the distillation proceeds. Beginning condensate will appear at different still head temperatures depending upon the character of the hydrocarbon being distilled. For example with coal tars the beginning still head vapor temperature will vary from 7 5 to C., with heavy waxes it is about C. and with pitches it varies from to C. The maximum still head vapor temperature is 345 C. in the case of tar, and 360 C. in the case of other high boiling hydrocarbons such as pitch.

One of the advantages of the invention is that lower still head temperatures can be used. In the present invention it has been found experimentally that when operating on tar, 70 percent of the tar can be recovered as distillate in 12 hours usmg a maximum still head temperature of 345 C. whereas in the prior art the recovery was only 50 percent and the maximum still head temperature was 355 C. After passing through the still the recirculating gas carries with it condensible and a very small proportion of non-condensible distillation products. The condensible distillation products are next condensed, a system being used which will avoid clogging of the condensers.

it has been found best to accomplish the condensation by a series of expansion and cooling steps, desirably accomplished by bathing. The distillate passes through uptake 37 from the still (through two-way valve 75 in open position to the condenser) to expansion condensing chambers 38, 40 and 41. The distillate enters condenser 38 through constriction 37. :9.

Each of the expansion condensers 38, 40 and 41 has bafiles 42 internally placed to contact the gases as they move upwardly and is provided with a cooling coil 43 through which cooling medium, suitably water, is circulated to cool the gases coming in contact with the coil. From the top of expanding condenser 38, the recirculating gas and residual uncondensed products are taken by a pipe 44 having a constriction 44' to the bottom of the next condenser .40 and from the top of condenser 40 the gases are taken by pipe 45 having a constriction 45 to the bottom of condenser 41. If the pipes 37, 44 and 45 are small enough, the pipes themselves will provide the constriction, but it is better practice to use large pipes and insert walls having constricting orifices.

The cross section of the condensershould be at least 100 times the cross section of the preceding constriction, and for best results'it should be at least 160 times the cross section of the preceding constriction. It is not considered desirable to use a cross section of the expanding condenser more than 500 times that of the constriction. The height of the expanding condensers is desirably greater than the cross section.

It has been found experimentally that the expansion and concurrent cooling greatlyaids in removing the heavy condensible vapors from the gas. At the bottom of each of the expansion condensers is a sump 46 which is drained through a valve 47, 48 and 50 to apipe 51 connected through valve 52 to one of a series of collecting tanks 53.

It will be understood that after the distillation proceeds, the character of the condensate changes and it will be deposited in a diiferent tank as the character changes.

A scrubber 54 is optionally interposed after the last expansion condenser 41, the last expansion condenser being connected through pipe 55. The gas and hydrocarbons desirabiy pass upwardly in the scrubber through checker work 56 against a countercurrent flow of scrubbing oil introduced by spray 57 at the top. The scrubb ng oil may be a petroleum oil such as is used for scrubbing coke oven gas. The scrubber is cooled if desired by water coil 58.

In some cases the use of the scrubber will avoid the use of the final expansion condenser, although the number of expansion condensers will vary with the particular practice followed.

After the last expansion condenser or after the scrubber, if it be used, a pipe 60 carries the gas to a pump 61 (two-way valve 75 being set to connect to the pump). The pump normally receives the gas on its inlet side at substantially atmospheric pressure and discharges the gas toward the recuperator at a slight super-atmospheric pressure, suitably of the order of one inch of mercury per foot of tar or other hydrocarbon. The temperature of the gas as it reaches the pump will suitably be between ambient temperature and 45 C. After the gas leaves the pump it is suitably further treated to remove water which may remain. This is accomplished by passmg the gas through pipe 62 to expansion chamber 63 and v thence through pipe 64 to water trap 65, having a valved drain 66 to tank 67. Expansion chamber 63 is dralned to valved drain 66 by pipe 63'. From the water trap gas passes through pipe 68 controlled by valve 70 back to the inlet pipe 33 of the preheater during the first stage of the operation and as long as condensible products come off from the heavy hydrocarbons.

A connection which can be opened to atmosphere s provided through pipe 71 and valve 72. Valve 72 is normally closed.

In starting up the operation, air enters with the charge of hydrocarbon, and the charge of air continues recirculating, the oxygen being changed to oxides of carbon and water.

During the distillation of coal tar through the creosote and anthracene ranges the products resulting from the process of the invention are similar to those in the prior art except for the advantages of higher quantities of.

distillate produced, lower temperature and, less destructive distillation, but beyond the anthracene range a ditler: ent character of product is obtained, which, as later e,X-.

plained, greatly increases the advantages of the invenlion. without limiting to any particular theory, it would appear that a factor in the creation of the different character of product may be the continuous recirculation of the gas which supplies the distillation heat, which brings back with it some quantity of non-condensible hydrocarbons which react to create the improved product during the subsequent recirculation cycles. it would seem that the major factor in creating the improved product is the rapid removal of the higher boiling constituents 1 before polymerization progresses;

ofi'from the heavy hydrocarbons, a peculiar change takes place in the character of the residue, which I have designated setting. The residue becomes porous and friable and assumes a firm but fragile structure and ceases to exhibit fluid or plastic properties. This condition can be observed by noting the drop in vacuum at the vapor outlet of the still caused by the increase in internal gas pressure resulting from the breaking up of the small amount of hydrocarbons remaining into non-condensible gas because of the high heat of the still which is now at a temperature of 900 to 1000 C.

When setting has occurred, the first stage of the distillation is over. Valve 72 is then momentarily opened to waste the recirculating gas or discharge it from the system and then valve 72 is closed, valve 70 is closed and valve 73 is opened in branch pipe 74 connected to a gas collector or other gas distribution and collecting system. At the same time the condensers are cut out of operation by turning two-way valves 75 and 75' in the directions to connect upcomer 37 to cross connection 76 and then to pump 61. At this stage coke residue in the still will normally have reached a temperature of about 900 to 1000 C. corresponding to that of the preheating gas. The coke will now give off spontaneously about 12 cubic feet per gallon of combustible gas of about 400 B. t. u. per cubic foot which is mostly noncondensible hydrocarbons. The heat developed from this gas can be used to fire furnace 27 and will supply approximately /6 of the total heat required in the process.

The pump 61 continues to function to draw off the hydrocarbon gas and carry it to the gas collector. I

As soon as the evolution of hydrocarbon gas ceases, the second stage of the process is over and the third stage is ready to begin. At this stage valve 72 is opened and left open, the preheater is not operated, and raw unheated or heated air or steam is brought in and passed through the coke in the still under the action of pump 61. A combustible gas is produced which can desirably be discharged through pipe 74 and valve 73 into a gas holder or other gas distribution system, and can, if desired, be mixed with the gas of stage 2. The bypass 76 remains open in stage 3. The gas produced in stage 3 is a mixture of hydrocarbons and carbon monoxide and bears an analogy to water-gas having about the same B. t. u. content.

The complete cycle on coke oven tar requires about 12 hours as against 24 hours in the prior art, employs a still head temperature of about345 C. and a pump temperature of 45 C. maximum, producing about 70 percent condensate as compared with 50 to 60 percent in the prior art processes.

Figure 6 illustrates schematically a commercial plant by way of example for carrying out the process as described in connection with Figure 4.

Air is introduced by a combustion air fan 77 through a pipe 78 to a burner 80 which receives coke oven gas through a pipe 81. The burner is conveniently located at the top of a recuperator 82 having the usual separate passages for combustion gases and gases to be heated. The combustion gases pass out through a stack 83. The gas to be recirculated is drawn in to the passages for gas to be heated atthe bottom of the recuperator as later explained, passed through these passages in heat transfer relation with the countercurrent flue gases and passed out at the top by pipe 84 through suitable ex pansion joints 85 and two-way valve 86 set in the proper direction to connect the tuyeres in the botoms of coke receptacles 87 in sealed contact at the bottom of the still 88. The coke receptacles are suitably mounted on dump cars 90 which move on a suitable track when the receptacles are detached from the bottom of the still. The recirculating gas enters preheater tubes 91 which keep the recirculating gas separate from the stack gas while it is in heat transfer relation with the fuel gases. The recirculating gas from the preheater enters the recuperator at the bottom by pipe 92 and valve 93. An alternate manner of recirculating gas flow to the recuperator, not going through the preheater, is by pipe 94 through two-way valve S5.

From the top of the still the distillate passes through pipe 96 and valve 97 to expansion condenser 98. A relief valve 100 is provided in pipe 96 and a valved connection 101 to atmosphere is also provided. A tar inlet for make-up is located at 102 above the still.

The expansion condenser 98 suitably has multiple parallel tubular paths and has the cross sectional relationship to the inlet constriction 103 already described. Water at the desired temperature is provided to cool ,condenser 98 from pipe 104 through valve 105, the

water connections being shown with dotted lines to the various condensers.

The condensate from condenser 98 enters receiver 106, and is withdrawn through pipe 107 and seal pot 108 by valved connection 110. Waste water is withdrawn from the separate water jacket of the condenser by pipe 111 to waste water drain 112, the waste water connections being shown in dash-dot lines.

Steam is received to the plant through steam line 113 and passes to receiver 106 to maintain the same at the desired temperature through pipe 114 and flows to the drain through pipe 115 and trap 116. Steam passes to the seal pot from pipe 114 by pipe 117 and from the seal pot by pipe 118 to pipe 115.

Steam is admitted to water heater 120 by pipe 121 and returns to the drain from the water heater by pipe 122 and trap 123. Water to the water heater is brought in through valved connection 124 and heated water leaves the water heater to pass through cooling water pipe 104 by valved connection 125. Thus the condenser water can be heated as desired.

From the first receiver 106 the overhead fraction passes by pipe 126 to expansion condenser 127 through constriction 127 which bears the proper relation to the condenser cross section as already explained. The condenser will suitably have multiple paths as in condenser 98. Cooling water passes in heat transfer relation with the condenser tubes as shown, entering by pipe 123 and leaving to flow to the drain by pipe 130. The condensate from condenser 127 collects in receiver 131 and is withdrawn through pipe 132 to seal pot 133, the condensate being drawn ofE by valved connection 134. Steam to heat the receiver enters from steam line 113 through pipe 135 and leaves through pipe 136 to trap 137 and thence to drain 112. pipe 133 to seal pot 133 and leaves the seal pot through pipe 140.

The overhead fraction from receiver 131 travels by pipe 141 through constriction 14-2 to condenser 143 suitably provided with multiple parallel paths for the condensate. The constriction bears the relation to the condenser cross section as already described. Water enters the condenser in heat transfer relation with the material to be condensed through pipe 144 and leaves through pipe 145 to drain 112. The condensate collects in receiver 146 and flows from the receiver by pipe 146 to seal pot 147 and thence is withdrawn through valved connection 148. Steam enters the receiver 146 from pipe 150 and leaves through pipe 151 to trap 152 and thence to drain 112. Steam enters the seal pot through pipe 153 and leaves through the trap 152 to the drain by pipe 15a.

The overhead fraction from receiver 146 passes by pipe 155 to scrubber 156. The scrubber is supplied with wash oil by pump 157 feeding the wash oil through pipe 158 to spray 160 in the top of the scrubber. The wash oil from the scrubber is carried by pipe 161 to receiver 162 which connects by pipe 163 with pump 157.

The non-condensible material from the scrubber is carried by pipe 164 to circulation pump 165. A cross connection pipe 3.66 passes from pipe 16 through valve 167 to the initial overhead pipe 96 the still. From the recirculation pump the gas passes through pipe 168 equipped with relief valve 170 to water collector 171 and thence bypipe 172 through two-way valves 95 and 173 set for flow to the preheater 91.

Steam flows from I An alternative path to the recuperator without going through the preheater is through two-way valve set for flow through by-pass 94. Pipe 174 is used to introduce air or steam under suitable pressure in the later stages of the cycle to the coke pot as earlier explained, by shifting two-way valve 86. Recirculating gas may be wasted to the atmosphere or carried to the gas holder through pipe 175 by shifting two-way valve 173.

In operation the system as shown in Figure 6 is the same asthat shown in Figure 4, there merely being provision for. the usual commercially used components in-Figure 6, which have been omitted to clarify the discussion in Figure 4.

- It is considered that in the best embodiment of the invention .the batch process is replaced by a semi-continuous process employing two or more stills for one set of condensers. Thus while one still is distilling condensate into the condensers at the first stage of the cycle, the other still can go through the second and third stages of the cycle. As soon as the other still has completed the third stage and been discharged and recharged, the first still will have completed the first stage and the condensers can be used on the newly charged still operating on the first stage.

With hard pitch (300 F.) as the starting material, about 35 percent distillate is obtained and about 55 percent coke, the distillate being almost all heavy dark waxlike resins melting over F.

v The coke resulting from the invention at the end of the process is a porous, friable coke of volatile content less than 1 percent and readily removed from the retort.

The end product coke constitutes about 20 percent of the coal tar and about 55 percent of the coal tar pitch distilled.

The coke of the invention produces superior silicon carbide for cutting wheels and can be used for carbon electrodes and for chemical carbon.

Whereas the coke obtained in beehive and slot type ovens by distilling pitch is hard and ditficult to crush, the coke obtained in the present process can be readily crushed and can be obtained readily with volatiles of less than 1 percent and with very low ash and sulphur.

Up through the creosote and anthracene ranges it appears that the products obtained from the distillation of coal tar in accordance with the present invention are generally similar to those produced in distillations in accordance with the prior art, but in the fraction above anthracene a new product is obtained which is a deep brown or black wax, to be distinguished from the light colored wax usually obtained, and referred to elsewhere herein as black wax.

The high heat of the heating gas releases the high boiling components above anthracene and the velocity of the heating gas through the material being distilled sweeps those high boiling components from the material being distilled before thermal decomposition sets in as would occur in the prior art with convection of heat through the liquid. If normal distillation practice Were employed on coal tar for example, at still head temperatures above 355 C., a fraction would come off leaving a residue of coke constituting about 30 percent of the tar. In accordance with the present invention, the black wax distillate is obtained and the coke constitutes only about 20 percent of the tar. It is thus obvious that more high boiling volatiles are removed by the process of the invention than by the prior art procedure, and that such higher boiling volatiles are essentially of difierent composition from those of the prior art. It has been found that less pyrolytic destruction or cracking takes place in distilling such higher boiling volatiles than in the prior art.

It has also been found that operations proceed at lower temperature in such higher boiling volatile range. The temperature employed in distilling a charge of black wax may rise to a maximum still head temperature of 350 C., preferably not over 330 C. The quantity of distillate in this case is about 58 percent of the material distilled.

The proportion of the black wax obtained in the present invention above the anthracene range of coal tar is 20 percent of the tar (50 percent of the tar comes off as oil). One of the unusual properties of the black wax of the invention is that it contains about 2 percent free carbon and has a melting point over 100 F.

The higher temperature distillates usually obtained in the prior art have been yellow in color, whereas the color of black wax obtained in the present invention is dark brown, often bordering on black. One of the very unusual properties of the black wax of the invention is that it thoroughly wets glass and metal, having excellent adherence.

The composition would appear to be distinctly difierent from that of the prior art high distillation products, probably due to reaction with recirculating unsaturated compounds carried by the neutral gas. The black wax of the invention is more resinous than the prior art product and provides a source of high molecular weight organic compounds.

The specific gravity of the black wax from one coal tar was about 1.2 at 60 F., and the softening point was 110 F. The flash point in a Cleveland open cut was about 196 C. and the firing point about 249 F.

Black wax provides a favorable crude from which to extract higher hydrocarbons such as acenapthene, chrysene, chrysogen, di-phenyl, methylanthracene, pyrine, fluourene, fluoranthrene and acridine. Black wax has a high dielectric strength characteristic of other coal tar derivatives. It is soluble in coal tar solvents such as toluol, xylol, naphthol and carbon bisulphide and is soluble in aliphatic ketone solvents such as acetone, methyl acetone and methyl ethyl ketone. On the other hand it is only slightly soluble in petroleum solvents such as gasoline, kerosene and Stoddard solvent. It is not soluble in methyl alcohol and ethyl alcohol. It is resistant to glycerine and resistant to ether. It makes an excellent corrosion resistant coating or decorative layer on metals, wood and fabric surfaces and is readily dissolved in coal tar solvents and ketone solvents as mentioned above. The remarkable adherence to metal and glass avoids the difiiculty through pin holing or bridging characteristics of many bituminous paints and the high ductility at low temperatures makes it possible to bend metal after painting.

Black wax is useful as a fireproofing coating because of its high flash point.

It will be evident that the present invention, therefore, makes possible the production of valuable products, which previously were not obtainable from heavy hydrocarbons.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the process, structure and product shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. The process of distilling high boiling hydrocarbon having a boiling point above 200 C. to obtain increased yields and yields of material not otherwise obtainable, which comprises maintaining a pool of the high boiling hydrocarbon in a closed space, recirculating a neutral gas substantially free from combustion gas and predominantly consisting of nitrogen, continuously through the pool of high boiling hydrocarbon in a system closed during the distillation cycle, preheating the gas to a temperature of between 800 and 1400 C. before it enters the hydrocarbon, passing the preheated gas through the pool of high boiling hydrocarbon and heating the hydrocarbon wholly by the heat of the gas and evolving distillate at a maximum still head end temperature in excess of 250 C. and not in excess of 360 C., condensing the condensible distillation products in the gas into at least two fractions of distinct boiling ranges, returning the gas and non-condensed products for reheating, and continuing to recirculate the gas through the high boiling hydrocarbon in accordance with the above procedure until condensible distillate substantially ceases and the residual product sets in the form of a coke.

2. The process according to claim 1, which comprises expanding the recirculating gas leaving the high boiling hydrocarbon and the distillation products of the high boiling hydrocarbon and then condensing the condensible distillation products in the gas into at least said two fractions of distinct boiling ranges.

3. The process according to claim 2, which comprises subsequently discontinuing the recirculation of the gas through the residue and then collecting a gaseous efiluent given off spontaneously by the residue.

4. The process of distilling according to claim 2, which comprises subsequently discontinuing the recirculation of the gas through the residue, then collecting a gaseous effluent given off spontaneously by the residue, and then flowing air through the heated residue and collecting the gas thus formed.

5. The process of distilling according to claim 2, which comprises subsequently discontinuing the recirculation of the gas through the residue, then collecting a gaseous efiluent given off spontaneously by the residue, and then flowing steam through the heated residue and collecting the gas thus formed.

References Cited in the file of this patent UNITED STATES PATENTS 145,707 Wilkinson Dec. 16, 1873 1,253,747 Thomas Jan. 15, 1918 1,257,199 Dundas Feb. 19, 1918 1,307,280 Walker June 17, 1919 1,418,893 Weiss June 6, 1922 1,687,595 Shore Oct. 16, 1928 1,848,051 Subkow Mar. 1, 1932 1,959,714 Govers May 22, 1934 1,991,750 Keeling Feb. 19, 1935 2,203,645 Reynard June 4, 1940 2,244,636 Atwell June 3, 1941 2,389,636 Ramseyer Nov. 27, 1945 

1. THE PROCESS OF DISTILLING HIGH BOILING HYDROCARBON HAVING A BOILING POINT ABOUT 200* C. TO OBTAIN INCREASE YIELDS AND YIELDS OF MATERIAL NOT OTHERWISE OBTAINABLE, WHICH COMPRISES MAINTAINING A POOL OF THE HIGH BOILING HYDROCARBON IN A CLOSE SPACE, RECIRCULATING A NEUTRAL GAS SUBSTANTIALLY FREE FROM COMBUSTION GAS AND PREDOMINANTLY CONSISTING OF NITROGEN, CONTINUOUSLY THROUGH THE POOL OF HIGH BOILING HYDROCARBON IN A SYSTEM CLOSED DURING THE DISTILLATION CYCLE, PREHEATING THE GAS TO A TEMPERATURE OF BETWEEN 800* AND 1400* C. BEFORE IT ENTERS THE HYDROCARBON, PASSING THE PREHEATED GAS THROUGH THE POOL OF HIGH BOILING HYDROCARBON AND HEATING THE HYDROCARBON WHOLLY BY THE HEAT OF THE GAS AND EVOLVING DISTILLATE AT A MAXIMUM STILL HEAD END TEMPERATURE IN EXCESS OF 250* C. AND NOT IN EXCESS OF 360* C., CONDENSING THE CONDENSIBLE DISTILLATION PRODUCTS IN THE GAS INTO AT LEAST TWO FRACTIONS OF DISTINCT BOILING RANGES, RETURNING THE GAS AND NON-CONDENSED PRODUCTS OF REHEATING, AND CONTINUING TO RECIRCULATE THE GAS THROUGH THE HIGH BOILIN HYDROCARBON IN ACCORDANCE WITH THE ABOVE PROCEDURE UNTIL CONDENSIBLE DISTILLATE SUBSTANTIALLY CEASES AND THE RESIDUAL PRODUCT SETS IN THE FORM OF A COKE. 